For purposes of this application, the present invention is discussed in reference to dental applications, but the discussion with respect to dental repair, regeneration or reconstruction is merely exemplary. The present invention is applicable to any context and application that may require self-healing composites.
Dental composites have improved over time. One of the first known dental composites was made with silicate cement. A problem with silicate cement was that it required extreme accuracy during preparation to ensure such a restorative would remain as long as possible. Poorly-made silicate cement restoratives could get destroyed even under the influence of saliva. Another problem with silicate cement was discoloration. Silicate cement absorbs food dyes and tends to yellow over time.
Silicate cement was soon replaced by dental acrylic plastics. Dental acrylic plastics often led to multiple complications, such as pulpitis and periodontitis. Pulpitis is tooth decay that penetrates through the enamel and dentin to reach the pulp of a tooth and periodontitis is any number of inflammatory diseases that affect the tissues surrounding and supporting a tooth. Additionally, acrylic plastics were difficult to polish. Amalgams were an improvement over dental acrylic plastics, but have been shunned by many because of their mercury content.
Metal-based amalgams, then porcelain or other ceramic materials, were used in a variety of remedial dental procedures. Synthetic composites are used as practical alternatives to these materials for such procedures. Synthetic composites typically include a resin with at least one additive to impart a desired property. The composite generally starts out as a paste or liquid and begins to harden when it is activated, either by adding a catalyst, adding water or another solvent, or photoactivation. Advantageously, synthetic composites provide an aesthetically more natural appearance versus porcelain or other ceramic materials.
Synthetic composites are typically made from complex mixtures of multiple components. Synthetic composites must be completely dissolvable in a fluid vehicle, yet remain flowable and viscous; undergo minimal thermal expansion during polymerization; be biocompatible with surrounding surfaces of tooth enamel and colloidal dentin; and, have aesthetic similarity to natural dentition in terms of color tone and polishable texture. Furthermore, synthetic composites must have sufficient mechanical strength and elasticity to withstand ordinary compressive occlusive forces, without abnormal wearing and without causing abrasion to dentinal surfaces.
The different varieties of synthetic composites may be approximately divided into three main groups of products: synthetic resin-based dental composites, glass-based dental composites, and hybrid dental composites.
A synthetic resin-based composite typically comprises materials such as silicate glass or processed ceramic that provides an essential durability to the composite. A synthetic resin-based dental composite typically comprises several monomers combined together. A monomer is a chemical that can be bound as part of a polymer. The synthetic resin-based dental composite includes other materials, such as silicate glass or processed ceramic that provides an essential durability to the composite. These materials may also be made from an inorganic material, consisting of a single type or mixed variety of particulate glass, quartz, or fused silica particles. Using differing types of inorganic materials, with differing diameter sizes or size mixtures, results in differing material characteristics.
Glass-based dental composites are made from glass particles, such as powdered fluoroaluminosilicate, dissolved in an aqueous polyalkenoate acid. An acid/base reaction occurs spontaneously, causing precipitation of a metallic polyalkenoate, which subsequently solidifies gradually. The glass particles may be made from silicate, such as silicone dioxide or aluminum silicate, but may also include an intermixture of barium, borosilicate, alumina, aluminum/calcium, sodium fluoride, zirconium, or other inorganic compounds. Some of the earlier glass-based composites were formulated to contain primarily a mixture of acrylic acid and itaconic acid co-monomers. However, more recently such hybrid products are modified to include other polymerizable components, such as hydroxyethyl methacrylate (“HEMA”) or 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (“Bis-GMA”).
Hybrid composites are the third category of synthetic composites. Similar to glass-based composites, hybrid composites are typically made from a combination of inorganic compounds and organic compounds, for example, glass particles with one or more polymers. Hybrid composites may comprise water-soluble polymers other than polyalkenoate, such as HEMA and other co-polymerizing methacrylate-modified polycarboxylic acids, which are catalyzed by photoactivation. Other hybrid dental composites may be modified to include polymerizable tertiary amines, catalyzed by reaction with peroxides.
Synthetic dental composites are increasingly used more often for dental procedures, such as restoration, reconstruction and repair, for example, fillings, crowns, bridges, dentures, orthodontic appliances, retainers, cements, posts and ancillary parts for dental implants to name a few. Most common, synthetic dental composites are used for anterior Class III and Class V reconstructions, for smaller size Class I and Class II molar reconstructions, for color-matching of cosmetic veneers, and for cementing of crowns and overlays. Nonetheless certain disadvantages of these materials have been noted. For example, the trace amounts of unconverted monomers and/or catalyst that may remain within the composite and, if subsequently absorbed systemically in humans, may be potentially physiologically harmful.
Most common, dental composites are used for reconstructions, color-matching, and cementing of crowns and overlays. Nonetheless, dental composites maintain certain disadvantages. For example, these composites tend to wear more rapidly. Perhaps the most significant disadvantage associated with dental composites is that they have a low resistance to disturbances such as cracks, breaks, fractures, splits, fissures, and gaps to name a few. Even relatively minor surface disturbances within the composite may progressively widen and expand, eventually resulting in partial or complete damage of the dental composite.
This low resistance to disturbances is also correlated with the proportional volume of the amount of synthetic composite required, or the lesser fraction of intact enamel and dentinal tooth material that remains available, prior to reconstruction, restoration or repair. It is well established from studies of the “cracked tooth syndrome” that once a damaging fracture has occurred, tooth loss may be almost inevitable, especially for carious teeth that have been previously filled. An improved synthetic dental composite having greater resistance to fracture would be significantly advantageous.
Synthetic composites having self-healing characteristics are known in the art, as illustrated for example in U.S. Pat. Nos. 6,518,330 and 6,858,659, describing self-repair of a polyester material containing unreacted amounts of dicyclopentadiene (“DCPD”) monomer stored within a polyester matrix resin, as sequestered within polyoxymethyleneurea (“PMU”) microcapsules. From a fracturing mechanical stress sufficient to cause rupturing of one or more microcapsule, the monomer is reactively released. As the monomer contacts the polyester matrix, a polymerization occurs. The in situ polymerization occurs as a result of a ruthenium-based Grubbs catalyst or Schrock catalyst, which may be incorporated into the matrix. Alternatively, the catalyst may be stored within a fraction of separately prepared microcapsules, or may be contained within the same material comprising the microcapsule outer wall.
Although a composite having self-healing characteristics is known in the art, there is still a demand for improved dental restorative formulations having self-healing characteristics, or the ability to automatically correct any disturbances, occurring in the composite as well as methods of making such restorative formulations. The present invention satisfies this demand.